The present invention relates to a cyrogenic storage container for storing helium, hydrogen, or neon. Typically, such cryogenic storage containers are used for shipping cryogens by sea transport for a journey that may extend anywhere from a month to forty days. As is well known in the art, heat transfer from the ambient to the liquid cryogen causes the liquid cryogen to boil off into a gaseous state. A point of time in some long journeys is reached at which the pressure of the cryogen exceeds the pressure rating of the cryogenic storage container., and thus, some of the cryogen is vented prior to reaching its destination. This results in loss of product and therefore adds to the expenses involved in the shipment of the cryogen. This is particularly true when liquid helium is to be transported. Additionally, when liquid hydrogen is transported, the venting of the hydrogen presents a danger due to its flammability.
Prior art cryogenic storage containers are designed to extend the point in time at which the cryogenic vapor must be vented for as long as possible. In one type of cryogenic storage container design, a pressure vessel is provided for containing the liquid cryogen. A vacuum vessel having an outer wall surrounding and spaced from the pressure vessel is provided for subJecting the space between the outer wall and the pressure vessel to a vacuum so that heat transfer by conduction is reduced. An inlet line communicates with the pressure vessel for filling the pressure vessel with the liquid cryogen and a vent line is also provided in communication with the pressure vessel for venting the boil-off vapor from the pressure vessel. An intermediate heat shield, provided between the pressure vessel and the vacuum vessel outer wall, is formed from a conductive material for intercepting the heat flow that would otherwise be transferred from the outer wall of the vacuum vessel to the pressure vessel. A pair of first and second insulation layers are provided between the heat shield and the vacuum vessel outer wall and the pressure vessel, respectively. Lastly, a liquid nitrogen container, containing liquid nitrogen, is provided in thermal contact with the intermediate heat shield for absorbing the intercepted heat by vaporization of the liquid nitrogen. This absorption of heat decreases the thermal load on the pressure vessel. A point is reached at which the vapor pressure of the nitrogen is greater than the rated pressure of the liquid nitrogen container and therefore, a vent line is provided to vent the nitrogen vapor. However, since the thermal loading on the pressure vessel is reduced, the contents of the pressure vessel can be stored for a longer time before having to be vented.
As will be discussed hereinafter, the present invention provides a cryogenic storage container for storing either hydrogen, helium, or neon in which the storage time is further enhanced over the container design discussed above.